1. Field of the Invention
The present invention relates to a method and apparatus to check the acceptableness of the state of wear in the covering fabric of a driving belt, said apparatus being of the type comprising:
an electrically conductive bearing structure; PA0 at least a first and a second electrically conductive pulleys rotatably engaged to said bearing structure; PA0 a driving belt operatively engaged on said pulleys and having a body provided with a reinforcement fabric on the work surface thereof designed to act in contact with said pulleys. PA0 applying a predetermined electric voltage between at least the first pulley and the second pulley in order to achieve an electric current passage along the belt stretches "A", "B" comprised between said first and second pulleys, said pulleys being electrically insulated with respect to each other; PA0 measuring one electric resistance value offered by the belt stretches "A", "B" on passing of said electric current; PA0 comparing said first resistance value with a predetermined electric resistance value corresponding to a given state of wear of the belt fabric. PA0 an electrically conductive bearing structure; PA0 at least a first and a second pulleys which are electrically conductive and rotatably engaged to said bearing structure; PA0 a driving belt operatively engaged on said pulleys and having a body provided with a reinforcement fabric on the work surface thereof designed to act in contact with said pulleys, said method further comprising: PA0 an electric circuit having the respective poles electrically connected to the first pulley and second pulley in order to apply electric voltage to the belt stretches "A", "B" kept taut between said pulleys, said at least first and second pulleys being electrically insulated with respect to each other; PA0 a measuring instrument for the electric resistance, associated with said electric circuit and designed to carry out the measuring of the electric resistance exhibited by the belt stretches "A", "B", conductive fillers being associated with said reinforcement fabric, designed to make said fabric electrically conductive; PA0 electronic means designed to compare the electric resistance values detected by said instrument with predetermined values corresponding to given wear conditions of the belt; PA0 alarm means designed to signal when said electric resistance values correspond to said predetermined values.
The method and apparatus in question can be used on driving belts of different kinds such as for example toothed belts, V-shaped belts, flat grooved belts and so on.
In the course of the present description reference will be particularly made, by way of non-limiting example only, to the use of the inventive method and apparatus for carrying out the checking of the state of wear in toothed belts.
2. Prior Art
It is known that driving belts and in particular toothed belts are used to transmit rotational movements from a toothed driving pulley to toothed driven pulleys.
Toothed driven pulleys control the movement of the mechanical members that, due to their operation, need to rotate in timed relationship with other mechanical members taking in rotation of the toothed driving pulley.
The concerned toothed belts substantially consist of a main body made of elastomeric material in which inextensible cords circumferentially disposed in side by side relation with respect to one another, are buried.
Internal to the annular configuration of the belt there is a number of teeth circumferentially distributed according to a predetermined pitch, which define the work surface of the belt and are designed to mesh with corresponding toothings offered by the pulleys.
The teeth, formed from part of the elastomeric material belonging to the main body, are greatly submitted to stresses, due to the thrust action transmitted to them by the toothing of the driving pulley and the thrust action they apply to the toothings of the driven pulleys.
In order to give the teeth the necessary strength so that they may withstand said stresses and the resulting wear phenomena, in many cases the work surface of the belt is covered with a reinforcing fabric also performing the function of protecting the elastomeric material against the action of chemical substances or other external agents with which the belt could be brought into contact.
This reinforcing fabric is directly exposed on the inner surface of the belt and is therefore the only element acting in contact with the pulleys.
As can be easily understood, during the belt operation the fabric will be subjected to a wear action that will bring about a gradual reduction in the thickness of the same and, as a result, a reduction in its capability of withstanding stresses.
This wear action, if extended in time, can lead to the reinforcing fabric tearing and therefore to the breakage of some teeth or even of the belt.
In most cases the foregoing inconvenience would cause important damages to the mechanical members driven by the belt in timed relationship.
Presently the only method enabling the state of wear or the impending breakage of a toothed belt to be verified is visual control.
Said visual control, in almost all of the cases, can be made only by dismantling the belt from the equipment to which it belongs, which involves the removal of many mechanical parts necessary to the operation and protection of the belt.
Another solution consists in periodically replacing the driving belts at regular intervals, but in this case belts which are not yet completely worn are almost always discarded.
In order to avoid the unexpected breakage of a belt it has been found possible to resort to a method and apparatus for checking the state of wear in the reinforcement fabric of a belt by verifying the electrical resistance variations in the fabric comprising conductive fillers.